SR268 Drainage planes and their applicability in New Zealand (2018)

Drainage planes are a new class of product that can sit behind a wall cladding and form a cavity. Drainage planes offer designers more freedom in cavity wall design and potential cost savings compared with traditional timber cavity battens.

The BRANZ drainage plane study detailed in this paper was funded by the Building Research Levy. The purpose of the study was to understand how drainage planes would perform when faced with the construction styles and climate found in New Zealand. Specifically, we aimed to clarify where drainage planes belong in the risk matrix of the Acceptable Solution to Clause E2 External moisture (E2/AS1) of the New Zealand Building Code.

The conclusions were that:

• the performance of drainage planes depends on the particular type of product
• drainage planes need windows to be flashed in a similar way to direct-fix claddings
• the proprietary nature of drainage planes may be unsuitable for E2/AS1 and would then need to be treated as Alternative Solutions
• if drainage planes were to form part of an Acceptable Solution (E2/AS1), the minimum finished cavity thickness in E2/VM1 would need to be changed to 10 mm
• the cavity formed by most drainage planes is robust enough to prevent insulation bulging and blocking the drainage path.